1. Field of the Invention
This invention relates to a storage system, generally connected to a host device, which performs data input/output online in response to instructions from the host device, and in particular relates to a technique for sorting data accumulated in the storage system.
2. Description of the Related Art
In an information processing system having a host device and a storage system which performs input and output of data online with the host device, as the number of accesses of data within the storage system by the host device increases, the order of arrangement of data within the storage system is gradually disrupted. The execution as necessary of processing to sort data within the storage system, organizing the data according to certain key information, prevents a decline in the speed of data retrieval in the storage system and is important for maintaining a high speed in data input/output from and to the host device. For example, in a bank information system, sort processing to organize customer account data according to, for example, account numbers, customer names or other key information, must be performed at appropriate times.
In the database processing system disclosed in Japanese Patent Laid-open No. 8-272592, a host processing device is connected to a data processing device which performs database processing and a disk device which stores data. The data processing device incorporates a database processing device and a sort processing device, and by this means sort processing and database processing can be performed in parallel. After the end of sort processing, the host processing device performs batch reads of sorted data from the data processing device, and outputs this data to the disk device.
At present storage system capacities are expanding, and the number of backup and sort operations to be performed are increasing. In particular, sort processing employing conventional technology is accompanied by frequent input/output operations between the host device and the storage system. As the number of sort operations increases, the number of input/output operations between the host device and the storage system grows. As a result, there is congestion of the communication channel between the host device and the storage system, the efficiency of use of cache memory in the storage system declines, time loss and other problems arise due to contention for access of the same physical storage devices (for example, hard disk drives) within the storage system, and the time required for input/output processing lengthens. As a result, in addition to the increased time required for the sort operation itself, there is an increase in the time required for backup processing. In general, sort processing and backup processing are performed at nighttime or other times when online service is halted, in order not to affect online service. Even so, however, if the time required for data sorting and backup processing is further lengthened, so that for example the time for resumption of online service is delayed, there is the danger of seriously impeding the operation of the information processing system. Particularly in the case of 24-hour online service, there is a need for technology enabling execution in parallel of sort processing without affecting data input/output in online transactions.